Algorithm And Simulation Implementation Of Topology-independent Time Division Multiple Access In Ad Hoc Networks

With the characteristic of highly dynamic topology, multi-hop communications, unstable wireless link, severe interference, and insufficient bandwidth resources of Ad hoc network, it presents a challenge in designing a media access control (MAC).Proposing a topology-independent time division multiple access (TDMA) based MAC protocol. The protocol divides time slot into priority phase, competition phase, transmission phase and response phase. Node can reserve channel through RTS/CTS in the priority phase of its allocated time slot. If the allocated time slot is idle, the other nodes may compete the slot in its competition phase through prioritized competition. Data frame cached in the queue of node is arranged in order of priority. The priority of the first frame to be transmitted represents the priority of the node. High-priority node is set lower backoff access time so as to get the priority of access channel. If node successfully reserving the, it sends data in the transmission phase.Serious interference and insufficient wireless channel bandwidth resources make ad hoc a channel capacity limited network, while multiple-input multiple-output (MIMO) technology can effectively increase the channel capacity. Collaborative communication can greatly reduce the probability of interruption of data transmission, and avoid retransmissions so that it can contribute in solving the problem of link instability of multi-hop wireless ad hoc network. On the basis of topology-independent time division multiple access MAC protocol, the thesis proposes a MAC protocol that is suitable for MIMO and collaborative communication. The sending node inform the receiving node of the number of streams it would like to send through RTS, and then receiving node estimates the information of streams that it may receive and can decode and send back the information through CTS. The information in the CTS helps the sending node making the decision of correct number of sending streams. All data frames of the network arrange in order of priority in the cache queue of node. The node learned of data frame transmission unsuccessfully would become the possible relay node of the frame. If the frame is in the first place of the possible relay node due to its priority is relatively higher than other frames, then the node automatically become the relay node of the frame. At last, if the receiving node receives the same frame relay/transmission requests, it will choose the node of the best channel state as the transmission node of this frame.To evaluate the effectiveness of the proposed protocols, this thesis conducts extensive simulations on NS-2 platform. The results showed that the proposed MAC protocols are effective.